In general, the reaction force control (the pedal effort control) of an accelerator pedal of an automobile includes making the pedal effort heavier when the accelerator opening exceeds a fuel-efficient point, or making it heavier during cruise control where the speed of an automobile is kept constant during operation without depressing the accelerator pedal so that the accelerator pedal functions as a footrest.
In addition, the reaction force control of an accelerator pedal of an automobile may include making the depression of the accelerator pedal easy in a sport mode. Patent Document 1 describes an accelerator pedal device which performs such a reaction force control.
The accelerator pedal device of Patent Document 1 includes an electronic control damper that generates a braking force toward the direction opposite to the depression direction of a pedal arm only when the depression angle of the pedal arm increases. A characteristic curve showing a relation between a braking force and a depression angle is determined such that the rate of increase of a set braking force decreases after the depression angle exceeds θ2, i.e., in the stage where the depression of the pedal arm approaches the limit.
Further, the accelerator pedal device of Patent Document 1 is set so that, in the characteristic curve showing the relation between the braking force and the depression angle, the braking force is reduced to the lowest level in the sport mode among other operation modes.
As described above, the accelerator pedal device of Patent Document 1 sets the braking force to be low in the sport mode, and thus it is easy to accelerate the engine smoothly to a high power output, and responsivity of the engine output to the depressing operation of the accelerator pedal (the pedal arm) improves. However, in a sport mode driving where loads of acceleration/deceleration, a centrifugal force during cornering, and the bounce with hard jolting are applied easily to the driver, it is necessary for the driver to conduct gentle operation while depressing the pedal arm, or necessary for the driver to drive the automobile while worrying about the possibility of change of the accelerator opening of the vehicle body, for example.
Further, the accelerator pedal device of Patent Document 1 shows a characteristic where the increase rate of the braking force decreases with an increase in depression of the pedal arm, and thus, it may be difficult for the driver to feel the limit of the characteristic of the engine itself and the sense of unity with the automobile, i.e., the driver cannot feel that he or she is operating the automobile.
In addition, as described above, the accelerator pedal device of Patent Document 1 is set so that the braking force is reduced to the lowest level in the sport mode among the other operation modes, for example, a normal mode or an environmentally friendly mode.
In other words, the accelerator pedal device of Patent Document 1 is set so that the braking force is larger in the normal or environmentally friendly mode than in the sport mode.
However, even during a normal driving where the operation mode is the normal or environmentally friendly mode, rapid acceleration is required in some cases, for example, in passing a front vehicle. In such a situation, it is difficult to depress the pedal arm, and thus the driver may possibly feel stress.
Furthermore, Patent Document 2 suggests an accelerator pedal device controlled by using a reaction force, in particular, a viscosity reaction force, of the accelerator pedal, and an automobile including this accelerator pedal device.
According to the accelerator pedal device and the automobile including the same of Patent Document 2, a reaction force rise curve showing a relation between the pedal reaction force and the pedal position (see FIG. 11 in Patent Document 2) is used as a control target of the pedal reaction force.
In this reaction force rise curve, the pedal reaction force quadratically increases with an increase in the pedal position, and thus the pedal effort is heavy when the depression of the accelerator pedal is fast.
Rapid acceleration is required in some cases, for example, in passing a front vehicle. However, in the above-described control disclosed in Patent Document 2, in such a situation, similarly to the problem of Patent Document 1, it is difficult for the driver to depress the pedal arm, and thus he or she may possibly feel stress.